Synthesis of chain-end functionalized polyolefins and polyolefin diblock copolymers via the combination of metallocene catalysts and reactive chain transfer agents

This paper discusses a facile route to prepare chain-end functionalized polyolefins containing a terminal functional group (OH, COOH, NH₂, etc.), and polyolefin diblock copolymers containing a polyolefin block and a functional polymer block. The chemistry is centered at an in situ chain transfer reaction during metallocene-mediated α-olefin polymerization using two reactive chain transfer (CT) agents, including dialkylborane (R₂B-H) and styrenic molecule/H₂, to form polyolefin containing a reactive alkylborane and styrenic terminal group, respectively. With the appropriate choice of metallocene catalyst, the polymer formed shows narrow molecular weight distribution (M_w/M_n∼2), and the polymer molecular weight is inversely proportional to the molar ratio of [CT agent]/[α- olefin]. In turn, the terminal borane group is very versatile in interconversion to various polar groups. More importantly, it can be quantitatively transformed to a living radical initiator for chain extension reaction with functional monomers. On the other hand, the terminal styrenic group was then selectively metallated and transformed to a stable polymeric anion for living anionic polymerization. The overall diblock copolymer process resembles a transformation reaction from metallocene-mediated α-olefin polymerization to a living free radical or a living anionic polymerization of functional monomers.